POLYSPHYGMOGRAMS 



293 



the time of the "a" wave, so that the latter finds the ventricle in a re- 

 fractory state (see page 178). The premature contraction is therefore 

 followed by a compensatory pause, which is evident on the tracing. An 

 example of such a case is given in Fig. 101. In doubtful cases the exact 

 site of origin of the premature beats can be determined only by careful 

 measurement of the distances between the various beats of the ventricle. 

 Whenever an irregularity repeats itself and the duration of one cycle 

 of the* arrhythmia accurately corresponds to another, the irregularity 

 may be due to: (1) premature auricular or ventricular contractions; 

 (2) the occasional occurrence of dropped beats (a failure of ventricular 

 response) ; or (3) a high degree of heart-block with a wide variation in 

 the ventricular response. The important point to note here is that, no 

 matter how irregular such a tracing may appear, if the irregularity re- 

 peats itself it can not be due to auricular fibrillation. 



Fig. 102. Paroxysmal tachycardia. The paroxysms start at xx following normal beats and 

 lasting for seven beats. The clue to "a," which falls with "v" after the first 



tions, is found in the initial beat of the new rhythm. (From E. P. Carter.) 



premature contrac- 



Paroxysmal Tachycardia and Auricular Flutter. These conditions are 

 characterized by a very great increase in the cardiac rate, the auricles 

 beating, in the case of paroxysmal tachycardia, at the rate of 150 to 200 

 per minute. In auricular flutter the rate is more rapid still, the auricles 

 attaining a speed of 200 to 400 beats per minute. (See Figs. 102, 103, 

 104.) There is no fundamental distinction to be made between these two 

 conditions; each is dependent upon impulses arising from an unusual 

 situation in the auricular muscle, the sinoauricular node having lost its 

 control over the auricular rate. The respective terms employed for the 

 designation of the two conditions are more or less arbitrary ones based 

 upon the extent to which the auricular rate is increased; the term par- 

 oxysmal tachycardia being applied to cases with the slower rates (150 

 to 200 per minute) whilst the term auricular flutter is employed in in- 

 stances where the higher rates of auricular contraction prevail. In 



